A hybrid vehicle includes a controller that manages the torque output of multiple prime movers, such as one or more electrical traction motors and an internal combustion engine. Driveline vibrations in such a vehicle are typically minimized by cancelling torque oscillations at a specific frequency or within a particular frequency range. Torque cancellation techniques may include passing driveline inputs through signal conditioning filters. This process can slow overall system responsiveness. Engine speed is typically used as a single feedback variable to command a corresponding control signal, for instance engine torque. However, single-variable feedback control schemes can provide inadequate vibration damping in a vehicle having multiple prime movers.
Another approach to minimizing driveline vibrations includes active driveline damping. In such an approach, desired powertrain and driveline operating states are determined. A motor damping torque is then calculated and added to a commanded motor torque in a manner that varies with the transmission operating mode. Damping torque and speed control are provided via a proportional-integral (PI) or a proportional-integral-derivative (PID) controller, as understood in the art, with the damping torque and speed control commands ordinarily decoupled with respect to each other.
That is, the gains required for driveline damping and speed control are separately calibrated and applied. A large rise or “wind up” in a given set point can occur, causing the integral (I) control terms from an integrator portion of a PI or PID controller to accumulate significant error. This may happen when the controller is calibrated in such a way as to be unstable or marginally stable, or when the proportional torque saturates against a limit. The integral torque continues to wind up to correct the error that is building, while at the same time the proportional torque cannot correct for the wind up.